The chemical element iron has the atomic number 26 and the symbol Fe (derived from the Latin ferrum). It is a metal found in group 8 of the periodic table and in the first transition series. It makes up a large portion of both the outer and inner core of the planet and is the most common element by mass, just ahead of oxygen (32,1 and 30,1 percent, respectively). It is the fourth most common element in the Earth's crust and has been deposited mostly by meteorites in metallic form, along with their ores.
Iron ores must be processed in furnaces that can reach temperatures of 1.500 °C or higher, which is about 500 °C higher than the temperature required to melt copper. People in Eurasia BC. The use of iron tools and weapons began in the second millennium BC, as he began to master this technique. It started to replace copper alloys in some places until the 1200s. It is accepted that the transition from the Bronze Age to the Iron Age took place during this period. Iron alloys such as steel, stainless steel, cast iron and special steels are the most widely used industrial metals today, due to their mechanical qualities and being economical.
As a result, the iron and steel industry is very important to the economy. Iron is also the least expensive metal, costing only a few dollars per kilogram or pound.
Pure iron surfaces are flawless and mirror-like silvery gray. Rust, also known as hydrated iron oxides, is a simple reaction between iron, oxygen and water. Rust takes up more space than the metal it is on and exposes the new surface to corrosion more than the oxides of some other metals, which exfoliate and form passivating layers. High purity iron such as electrolytic iron is more resistant to corrosion.
An adult human body contains 4 grams (0,005% of body weight) iron, most of which is found in hemoglobin and myoglobin.
These two proteins are crucial to vertebrate metabolism because they allow the blood to carry oxygen and the muscles to store oxygen. Human iron metabolism requires a minimal amount of iron in the diet to maintain appropriate levels. Several important redox enzymes involved in cellular respiration, oxidation, and reduction in plants and animals also contain iron as a metal in the active site.
Iron is most commonly found in the iron(II) and iron(III) oxidation states. Along with the two group 8 elements, ruthenium and osmium, iron has some properties in common with other transition metals. Iron can form compounds with oxidation levels ranging from 2 to +7. Iron can also form a variety of coordination compounds, some of which have important uses in industry, medicine or research, such as ferrocene, ferrioxalate, and Prussian blue.
Properties and Allotropes of Iron
Iron exists in at least four different allotropes, traditionally identified by the letters α, γ, δ, and ε.
The first three species can be seen under typical pressures. As molten iron cools below its freezing point of 1538 °C, it crystallizes into its allotrope, which has a body-centered cubic (bcc) crystal structure. At 1394 °C, it transforms into austenite, an allotrope of iron with a face-centered cubic (fcc) crystal structure. The crystal structure is converted back to the bcc-iron allotrope at 912 °C and lower temperatures.
Due to its importance in hypotheses regarding the cores of the Earth and other planets, the physical properties of iron at extremely high pressures and temperatures have also been studied in detail.
The hexagonally stacked (hcp) structure, also called “ε(Epsilon) Iron”, is formed when the pressure is greater than about 10 GPa and the temperature is less than or equal to a few hundred kelvins. The transition from the alpha phase at high temperature to epsilon iron occurs at a higher pressure.
There is some controversial experimental evidence to support the existence of a stable beta phase at pressures above 50 GPa and temperatures of at least 1500 K. It is expected to have a double HCP structure or an orthorhombic shape. (Confusingly, the word "-beta iron" is sometimes used to refer to -alpha iron above the Curie point when it changes from being ferromagnetic to being paramagnetic, although its crystal structure has not changed).
It is generally believed that an epsilon or beta iron-nickel alloy with (or) structure forms the Earth's inner core.
Boiling and Melting Points of Iron
The melting and boiling points of iron, as well as the enthalpy of atomization, are lower than those of previous 3D elements, from scandium to chromium, indicating that the contribution of 3D electrons to metallic bonding decreases as the 3D electrons are pulled more by the core into the inert core; however, the values of the previous element manganese are higher because this element has a partially filled XNUMX-dimensional subshell and as a result d-Ruthenium shows the same trend, but osmium does not.
For pressures below 50 GPa, the melting point of iron is well established experimentally. Data published for higher pressures since 2007 still differ by tens of gigapascals and more than a thousand kelvins.
Magnetic Properties of Iron
Below the Curie point, which is 770 °C (1.420 °F; 1.040 K), iron typically changes from paramagnetic to ferromagnetic when two unpaired electrons in each atom align with the spins of their neighbors to produce a general magnetic field. This is because these two electrons are not involved in metallic bonding and their orbitals are not directed towards nearby atoms in the lattice.
Atoms spontaneously split into magnetic fields about 10 micrometers wide in the absence of an external magnetic field source. Atoms in each domain have parallel spins, but some domains have different orientations. As a result, the overall magnetic field of a macroscopic piece of iron will be almost zero.
When an external magnetic field is applied, magnetization in the same general direction causes the fields to increase and strengthen the external field at the expense of those nearby pointing in other directions. Devices that need to channel magnetic fields to perform their design functions, such as electrical transformers, magnetic recording heads, and electric motors, take advantage of this phenomenon. Impurities, lattice defects, or grain and particle boundaries can “fix” fields in new positions, so the effect persists even after the external field is removed – thus turning the iron object into a (permanent) magnet.
Some iron compounds, such as the mineral magnetite, a crystalline form of the mixed iron(II,III) oxide Fe3O4, show similar properties (although the atomic-scale mechanism, ferrimagnetism, is slightly different). The earliest compasses used for navigation were lodestones, which are bits of magnetite with a natural permanent magnetic property. Before replacing cobalt-based materials, magnetite particles were widely used in magnetic recording media such as core memory, magnetic tapes, floppy disks, and disks.
Source: Wikipedia
📩 03/04/2023 20:59